the error you are getting suggests that there is a problem connecting to the database.
open the database tab, double click the connection and click the test button to make sure the connection is working.
you can fix the quote problem with HTML manually though, by removing the str_replace() function form the initial value
change the code for the initial value from:
<?php echo(str_replace('"', '"', $row_WADANL_Newsletter['NL_body'])); ?>
<?php echo($row_WADANL_Newsletter['NL_body']); ?>